.TH std::promise::set_exception 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::promise::set_exception \- std::promise::set_exception

.SH Synopsis
   void set_exception( std::exception_ptr p );  \fI(since C++11)\fP

   Atomically stores the exception pointer p into the shared state and makes the state
   ready.

   The operation behaves as though set_value, set_exception, set_value_at_thread_exit,
   and set_exception_at_thread_exit acquire a single mutex associated with the promise
   object while updating the promise object.

   An exception is thrown if there is no shared state or the shared state already
   stores a value or exception.

   Calls to this function do not introduce data races with calls to get_future
   (therefore they need not synchronize with each other).

.SH Parameters

   p - exception pointer to store. The behavior is undefined if p is null

.SH Return value

   \fI(none)\fP

.SH Exceptions

   std::future_error on the following conditions:

     * *this has no shared state. The error code is set to no_state.
     * The shared state already stores a value or exception. The error code is set to
       promise_already_satisfied.

.SH Example


// Run this code

 #include <future>
 #include <iostream>
 #include <thread>

 int main()
 {
     std::promise<int> p;
     std::future<int> f = p.get_future();

     std::thread t([&p]
     {
         try
         {
             // code that may throw
             throw std::runtime_error("Example");
         }
         catch (...)
         {
             try
             {
                 // store anything thrown in the promise
                 p.set_exception(std::current_exception());
                 // or throw a custom exception instead
                 // p.set_exception(std::make_exception_ptr(MyException("mine")));
             }
             catch (...) {} // set_exception() may throw too
         }
     });

     try
     {
         std::cout << f.get();
     }
     catch (const std::exception& e)
     {
         std::cout << "Exception from the thread: " << e.what() << '\\n';
     }
     t.join();
 }

.SH Output:

 Exception from the thread: Example

.SH See also

                                sets the result to indicate an exception while
   set_exception_at_thread_exit delivering the notification only at thread exit
                                \fI(public member function)\fP
